1. Technical Field
This invention relates generally to electrostatographic copiers and printers.
2. Background Art
Most high speed copiers and printers use a dry electrostatographic process to place toner particles on paper. The process generally includes the creation of an electrostatic latent image which is developed with toner particles sized between two microns and eighteen microns. The developed image is transferred to a receiver sheet and fused.
In Direct Electrostatic Printing (DEP), charged toner particles are "gated" through holes in a pixel-wise fashion directly to a receiver from a charged toner conveyor. In one known format, the toner conveyor has an electrode array comprising repeating sets of electrodes upon which an electrostatic traveling wave pattern is established.
The traveling wave pattern causes already charged toner particles to travel along the conveyor to an area opposite a series of printhead apertures which form an electrode array of individually addressable electrodes which selectively propel toner therethrough to the recording media.
In Direct Electrostatic Printing which uses an electrode array as a toner conveyor, the width of each of the electrodes for the traveling wave grid is typically no smaller than about 100 microns separated by 100 micron spaces, and is used to transport 10 micron toner particles; an order of magnitude difference. This difference causes toner particles to be transported in mass, referred to in the literature as "clouds" of toner. Transporting toner in mass negatively effects control over individual particles.
Another disadvantage of Direct Electrostatic Printing, is that apertures must be used to select particles from the toner clouds for directing to the recording media. Such apertures are subject to clogging.
Yet another disadvantage of Direct Electrostatic Printing, is that the recording media must be substantially spaced from the aperture by a gap that allows divergence of the toner particles before they reach the recording media. The gap also permits the toner particles to bounce off the surface of the recording media.